Volcanic eruption

Mechanism of destruction

Gradual or explosive eruption, ejecting hot ashes, pyroclastic flows, gases and dust. Blast pressures may destroy structures, forests and infrastructure close to the volcano and noxious gases may kill. Hot ash falls for many kilometers around the volcano, burning and burying settlements. Dust may carry for long distances, and fall as a pollutant on other settlements further away. Molten lava is released from the volcanic crater and may flow for many kilometers before solidifying. The heat of lava will burn most things in its path. Snow-capped volcanoes suffer ice-melt causing debris flows and landslides that can bury buildings. A volcanic eruption may alter the regional weather patterns, and destroy local ecology. Volcanoes may also cause ground upheaval during their formation.

Parameters of severity

Volume of material ejected. Explosiveness and duration of eruption, radius of fall-out, depth of ash deposit.

Causes

Ejection of magma from deep in the earth, associated with mantle convection currents. Tectonic processes of continental drift and plate formation.

Hazard assessment and mapping techniques

Identification of active volcanoes. Volcanoes readily identifiable by their topographical and geological characteristics. Activity rates from historical records and geological analysis. Seismic observation can determine whether a volcano is active.

Potential for reducing hazard

Lava flows and debris flows may be channelled, dammed and diverted away from settlements to some extent, by engineering works.

Onset and warning

Eruption may be gradual or explosive. Seismic and geochemical monitoring, tiltmeters, and mudflow detectors may be able to detect build up of pressure over the hours and days preceding eruption. Mud flow detection, geotechnical monitors and tiltmeters are some of the monitoring strategies available. Evacuation of population away from volcano environs is often possible.

Elements most at risk

Anything close to the volcano. Combustible roofs or buildings. Water supplies vulnerable to dust fall-out. Weak buildings may collapse under ash loads. Crops and livestock are at risk.

Main mitigation strategies

Location planning to avoid areas close to volcano slopes being used for important activities. Avoidance of likely lava-flow channels. Promotion of fire-resistant structures. Engineering of structures to withstand additional weight of ash deposit.

Community participation

Awareness of volcano risk. Identification of danger zones. Preparedness for evacuation. Fire-fighting skills. Taking shelter in strong, tire-resistant buildings.